In general, there are conduction, convection and radiation as a heat transfer mechanism. Conduction heat is mainly transferred by solid and convection heat is mainly transferred by fluid. In addition, radiation heat is transferred through a process of discharging energy formed of electromagnetic waves emitted from surface of a certain heating unit, in which heat is emitted at velocity of light even at a state of having no medium and is delivered directly to an object. Wavelength of the radiation heat ranges from an infrared ray region to an ultraviolet ray region whose wavelength is the shortest via a visible ray region. However, in comparison with the visible ray or ultraviolet ray, it has been known that a band of the wavelengths of the infrared rays such as far infrared rays, middle infrared rays, and near infrared rays has the strongest heating function.
Therefore, conventional cooking appliances using infrared rays have been developed in various forms.
One example of an existing infrared ray cooking appliance was disclosed in Korean Patent Registration No. 0779225 published on Nov. 28, 2007. The infrared ray meat grill cooker disclosed in the Korean Patent Registration No. 0779225 includes: an infrared lamp whose outer portion is composed of quartz tubes; a cooking pan that is placed over the infrared lamp; and a reflective board that is placed below the infrared lamp. The infrared ray meat grill cooker employs a uni-direction heating method in which the infrared lamp heats the cooking pan and the cooking pan grills only a lower portion of meat. As a result, the infrared ray meat grill cooker may cause inconveniences that meat must be turn over constantly in order to prevent the meat from being burnt excessively. In addition, a thermal efficiency may fall.
Another example of a cooking appliance developed using infrared ray technology was Korean Utility-model Registration No. 314605 published on May 27, 2003. The meat roaster disclosed in the Korean Utility-model Registration No. 314605 has a near-infrared ray lamp that is positioned at a certain distance over a gridiron grilling pan and a reflective board over the infrared ray lamp. The meat roaster applies near-infrared rays directly onto meat from the above infrared ray lamp and successfully keeps meats from burning. Accordingly, the meat roaster has an advantage that even the inner portion of the meat can be roasted evenly. However, the meat roaster also employs a uni-direction heating method in which the near-infrared rays emitted from the near-infrared ray lamp roasts only a portion of meat, to thereby cause inconveniences that meat must be turn over constantly in order to prevent the meat from being burnt excessively.
Moreover, in the case of these cooking pans using the infrared rays or near-infrared rays, there is a problem that time taken to roast foods put on the cooking pans delays. In addition, since the infrared ray lamps or near-infrared ray lamps should be turned on for a long time in order to heat foods put on the cooking pans, there is also a problem that an expense burden is additionally produced by increase of electric charges.
Meanwhile, still another example of an existing infrared ray cooking appliance was disclosed in Korean Patent Registration No. 833966 registered on May 26, 2008 by the same applicant as that of this application. The infrared ray radiation cooker disclosed in the Korean Patent Registration No. 833966 includes: a base stand at the center of the upper surface of which a shaft hole is formed, and on one side of which a power switch for controlling an electric power supply is formed; a rotating pan which is a circular plate style container which can contain food on the upper surface thereof, and at the center of the lower surface of which a shaft protrusion is formed so as to be detachably inserted into the shaft hole; a supporting pillar which is vertically placed at one side of the base stand; and an infrared ray irradiator which is placed on the upper end of the supporting pillar and which is switched by the power switch, to thus apply infrared rays onto the rotating pan.
The above-described infrared ray radiation cooker employs a bidirectional heating method in which the infrared ray irradiator irradiates infrared rays onto food put on the rotating pan, to thus roast the upper and inner portions of the food and the rotating pan that has been heated by radiant heat of infrared lamps of the infrared ray irradiator roasts the lower portion of the food. In comparison with the conventional uni-directional infrared ray cooker, the above-described infrared ray radiation cooker has advantages that a thermal efficiency is excellent, foods such as meat for roasting can be evenly roasted without excessive burning although they are not continuously turned over, and little amount of smoke or odor is produced during cooking. However, since the supporting pillar is placed at one side of the base stand in the structure of the above-described infrared ray radiation cooker, it is very inconvenient to take food put on the rotating pan at a direction that at least the base stand is placed. Therefore, it is a little inconvenient for several persons who sit around in a restaurant or family for example to use the infrared ray radiation cooker.
In addition, since meat is roasted using radiant heat that is irradiated by the infrared ray irradiator, a time difference occurs in a cooking time taken to roast the upper and lower portions of the meat in which the upper portion of the meat is roasted more quickly than the lower portion of the meat until the rotating pan is heated at an initial time of roasting the meat. Accordingly, although meat can be bidirectionally cooked in the infrared ray radiation cooker, consumers who want to eat roasted meat earlier are inclined to turn over meat in order to make the lower portion of the meat roasted earlier. In addition, in spite of an advantage that the lower rotating pan uses radiant heat induced from the upper heat emission of the existing cooker, consumers who are accustomed to use the conventional upstream heating cooker do not sufficiently use a function of bidirectionally roasting meat by using the upper heat emission and lower radiant heat use mechanism in the conventional bidirectional radiation cooker due to a time difference occurring in a cooking time taken to roast the upper and lower portions of food for an initial time of 1-2 minutes as well as a habitual attitude that is accustomed when using a general cooker of roasting meat.
Further, consumers have habits of awaiting until the lower rotating pan is heated by the upper heat irradiator before cooking food as in the case of using the existing upstream heating cooker. Accordingly, a lot of electric charges are additionally produced due to a delay in time that may occur by doing an unnecessary operation of awaiting until the lower rotating pan is heated by the upper heat irradiator before cooking food. In addition, consumers use a method of roasting food while turning over the food that is similar to a unidirectional heating cooker such as the conventional upstream heating cooker at an initial cooking time during cooking due to a time difference occurs in a cooking time taken to roast the upper and lower portions of meat, even in the bidirectional radiation cooker, and may feel uncomfortable at the initial cooking time because of awaiting until the lower rotating pan is heated by the upper heat irradiator before cooking food as in the case of using the existing upstream heating cooker.